The present invention relates generally to shafts adapted for connection to other shafts in a manner that transfers rotational movement. More specifically, the present invention relates to shafts bearing splines for facilitating such a connection.
Many situations exist in which it is desirable to transfer rotational movement of one shaft onto a second, coaxial shaft. For example, drive shafts may contain multiple coaxial shafts interconnected in a manner that transfers rotational movement of one shaft onto the other shafts. Frequently, one shaft in this arrangement will define a spline that includes a plurality of teeth designed to interact with recesses on the other shaft. The interaction between the teeth and the recesses effects the transfer of rotational movement between the shafts.
The teeth of the spline can take on a variety of profiles, and many examples of different profiles exist in the prior art. Unfortunately, the tooth profiles taught by the prior art confer poor fitting characteristics onto the shafts. These inadequate fit problems can result in inferior noise, vibration, and harshness (NVH) performance, relatively low durability, high plunge effort under torsional load, and significant weight. Most of these problems are related to a relatively low spline contact rate that results from the use of conventional tooth profiles. Frequently, the teeth of the spline in prior art devices have curved sides, which lead to very high compression stress on the teeth and the above-noted inadequate fit problems.
The present invention provides a shaft that bears a spline having a plurality of teeth, each having an optimized tooth profile. The tooth profile includes a straight portion in each of the two sides of the tooth. Furthermore, the dimensions of the tooth are optimized based upon various characteristics of the shaft, such as the outer diameter and the wall thickness.
In one embodiment, a shaft according to the present invention comprises a tube having an outer diameter and a spline comprising a plurality of teeth integrally formed by the tube. Each tooth has a top surface that includes at least one point that lies on the outer diameter of the tube. Furthermore, each tooth includes first and second sides, each of which has a straight portion disposed between top and bottom transition regions. The top transition region is preferably a curvilinear connection between the straight portion and the top surface, while the bottom transition region is preferably a curvilinear connection between the straight portion and the main body of the tube. The length of each straight portion is preferably between approximately 0.6 and 0.9 times the length of the side, which includes the top and bottom transition regions.
The present invention can be used in a variety of different shaft types, including drive shafts and half shafts in a vehicle axle. Drive shafts bearing a straight side tooth spline profile according to the present invention have demonstrated significantly improved performance in all of the problematic aspects listed above.